When you near the prison, make sure all pursuing vehicles are destroyed and park down the road a bit. Equip your Sniper Rifle and try to pick off the Authority goon on the turret above the entrance gate.

Another enemy is in the left tower. Sniping may take a few shots since they have helmets. Use the nearby rocks for cover.

Approach the door and hit the green panel to open the gate. Look for a hole in the ground on the other side and take the ladder down. Follow the path into the prison.

As soon as you enter the prison, search the side room before going down the stairs for the EMP GrenadesSchematic.

These grenades will knock out Authority enemy shields -- of which there are many in the prison. Proceed through the prison until you get to the laser gate. These are each tied to a Power Supply, the glowing blue column of light. You can damage this to destroy it with weapon fire, an EMP Grenade or melee attacks. Use your melee attack on this one since you can easily reach it.

In Authority Prison, after knocking out the first power supply to bring down the lasers, look for this card on the far side.

The first Authority enemies you encounter in the game are in this room. You have Mind Control Bolts which you can test out on the guard on the upper level, but you MUST hit him in the head. After this you can control your bipedal bomb.

The less-gimmicky Authority AV2x Rounds of the Authority Machine Gun are the best option for all of these enemies, though. A shielded guard also appears. You can use an EMP Grenade to immediately knock out his shield, or attempt to use your armor-piecing rounds to shoot through the small hole in the shield by the enemy's shoulder.

Knock out the Power Supply in this room and loot the area. In the next room, a laser gate and several more Authority enemies block your path. Enter the small room and look through the window for a Power Supply shoot it out and continue.

Soon you'll come to a Turret. A Power Supply next to it controls it. You can shoot this through the barred window. A series of Turrets follow -- watch for their lasers and you can avoid being seen. You can slip across the hallway and shoot the next Power Supply through a window.

Just before the first turret, a hole in the wall leads to this card. Disable the turret before going for the Giant Mutant Card.

You'll have to take cover right under the next Turret to get an angle on its Power Supply through the door. In the next room, use Authority AV2x Rounds to get some headshots on the various enemies. You can stock up on this awesome ammo in this very room.

Whack the Power Supply until it gives out and head through the laser gate. At the stop of the Stairs is the EMP Grenade Card, just to the right.

In the Authority Prison, just after the first three auto turrets you encounter, you'll come across an open room with a bunch of Authority and a shielded Authority. Break the laser grid here by taking out the Power Supply and then go up the stairs. Up here is the EMP Grenade Card.

Loot the next area for Feltrite (2) and supplies while fending off the Authority. Soon you'll come to a control panel overlooking a cell block. Hit the panel to unleash Mutants on the guards below. finish off the Mutants and head down to free Captain Marshall. Just hit the control pad on his cell door to free him.

After freeing Marshall from the Authority Prison, follow him down the stairs and look for a Grindable Lock. Open this to reveal the Marshall Card.

In the courtyard, try to use the explosive barrels. The biggest threat in this area, however, is a manned turret at the far end. Use the Sniper Rifle or, better yet Authority AV2x Rounds to hit the dude operating it. Slowly inch closer and loot the area as you move up.

When things quiet down, head up the stairs on the right side and pause just at the top. Look through the door past the turret and you should see the Power Supply. Shoot it and proceed around to let Marshall through the other side.

Now, take the turret and use it to mow down the Authority reinforcements from the dropships.

Marshall will eventually get through the door and then hotwire and elevator, leaving you to fend for yourself. Luckily, an Authority soldier busts through the nearby door creating an easy exit. before you leave, grab the Shield Guard card.

After you and Walter split ways in the Authority Prison, the Shield Guard Card is just on the other side of the door the Authority goon knocks down. This is right before you exit the prison in the Liberate Captain Marshall mission.